What Is It, Causes, Diagnosis, and More…
Author:Nikol Natalia Armata
Editors:Alyssa Haag,Ian Mannarino MD
Copyeditor:Sadia Zaman, MBBS, BSc
What is obstructive shock?
Obstructive shock refers to the anatomical obstruction of the great vessels of the heart (e.g., superior vena cava, inferior vena cava, and pulmonary vessels) that leads to decreased venous return and/or excessive afterload (i.e., the force that the left ventricle has to overcome to eject blood through the aortic valve), resulting in decreased cardiac output.
Shock describes circulatory failure and ineffective tissue perfusion that may lead to reversible, or if prolonged, irreversible cellular injury. There are four different types of shock: obstructive, distributive (including anaphylactic, septic, and neurogenic shock), cardiogenic, and hypovolemic shock. Shock is a life-threatening condition and requires immediate medical attention.
What causes obstructive shock?
There are two major causes of obstructive shock: a blockage of the pulmonary vascular system, thereby affecting the blood flow from the right-sided heart chambers to the left-sided heart chambers, as seen in significant pulmonary embolisms and severe pulmonary hypertension; or an extrinsic mechanical compression of the great vessels of the heart that alters the heart’s cardiac output. Examples of extrinsic mechanical compression include a tension pneumothorax, pericardial tamponade, restrictive cardiomyopathy, and constrictive pericarditis.
What are the signs and symptoms of obstructive shock?
A characteristic sign of causative conditions like pneumothorax and tamponade may include dilated and engorged neck veins, resulting from the inability of blood to return to the heart. Various constellations of signs may indicate a probable underlying cause. For example, hyperresonant sounds on percussion, distended neck veins, and absent breath sounds are typically indicative of tension pneumothorax. Distant heart sounds and decreased pulse pressure can usually indicate cardiac tamponade. Tension pneumothorax can mimic the signs of cardiac tamponade, with findings of distended neck veins and hypotension.
How is obstructive shock diagnosed and treated?
Obstructive shock can be diagnosed based on a thorough review of the individual’s medical history and physical examination. A detailed respiratory and cardiovascular examination is necessary in order to distinguish the underlying cause of obstructive shock. Arterial saturation may also be assessed, using a pulse oximeter, and can be decreased in cases of tension pneumothorax. Lab studies, such as a metabolic panel, lactic acid, arterial blood gas, or electrocardiogram (ECG) are often performed. Imaging studies, such as point of care ultrasound or CT scan, can also assist in assessing the underlying cause.
Importantly, if an individual is unstable, treatment is typically initiated before imaging has confirmed the diagnosis. The initial treatment for obstructive shock requires resuscitative measures and ABC (airway, breathing, circulation) assessment, which includes supplemental oxygen support and pressure support with intravenous crystalloids. However, fluids should be given with caution, and close monitoring is necessary as excessive administration of intravenous fluids may have a paradoxical worsening of hypotension due to severe right ventricular dilatation, which can affect left ventricular filling. If shock persists despite IV treatment, early initiation of vasopressors (e.g., norepinephrine, or vasopressin) is the first-line choice. The patient may also be intubated if indicated.
Further treatment options depend on the underlying cause of obstructive shock.
What are the most important facts to know about obstructive shock?
Obstructive shock refers to the anatomical blockage of the great vessels of the heart, leading to decreased venous return, increased afterload, and decreased cardiac output. Tension pneumothorax, pulmonary embolism, and cardiac tamponade are different causes of obstructive shock, all of which are considered medical emergencies. Individuals usually present with concerning symptoms, such as tachycardia, tachypnea, hypotension, chest pain, or distended neck veins. Diagnosis is mostly clinical, based on history and clinical presentation, although additional testing can be used to confirm the diagnosis. Initial treatment involves supportive care, administering IV crystalloids with caution followed by varied treatment options depending on the underlying cause.
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Resources for research and reference
American College of Surgeons. (2012). Advanced trauma life support: Student course manual (9th ed.). Chicago, IL: American College of Surgeons.
Bunin, J. (2017). Diagnosis and Management of Hypotension and Shock in the Intensive Care Unit. In C. Buckenmaier, & P. F. Mahoney (Eds.), Combat Anesthesia: The First 24 Hours. (1st ed., pp. 327–338). Office of the Surgeon General, United States Army.Standl, T., Annecke, T., Cascorbi, I., Heller, A. R., Sabashnikov, A., & Teske, W. (2018). The Nomenclature, Definition and Distinction of Types of Shock. Deutsches Arzteblatt international, 115(45): 757–768. DOI: 10.3238/arztebl.2018.0757